Optical fiber is a natural choice as the transmission medium for a trunk network, because trunk connections usually need a high transmission capacity, the transmission distances are long and often there are existing routes for cables. Even for subscriber connections (the line between the local exchange and the subscriber) the situation is rapidly changing, because various multimedia services that demand a high transmission rate will be delivered to the private consumer.
However, no great savings can be expected in the construction costs of the network which provides the future broadband services, because the costs are mostly due to the cable installation. On the one hand, it is desired that as much optical fiber as possible would be built on the subscriber network side as well, as it is evident that it will be needed in the future. On the other hand, the costs of renewing the subscriber network are extremely high, and the renewal will take decades. The high costs are thereby the worst obstacle in introducing the fiber on the subscriber network side.
It is because of the aforementioned reasons that studies are under way to determine the possibility of using the ordinary subscriber line (twisted pair cable) for high-speed data transmission, in other words, for speeds which clearly exceed the speed of the ISDN basic connection (144 kbit/s). The present ADSL (Asymmetrical Digital Subscriber Line) and HDSL (High bit rate Digital Subscriber Line) technologies offer new possibilities for high-speed data and video transmission via the telephone line to subscriber terminals.
The ADSL transmission connection is asymmetric so that the transmission rate from the network to the subscriber is significantly higher than that from the subscriber to the network. ADSL technology is mainly intended for various subscriber services (so-called "on-demand" services). In practice the speed of an ADSL transmission connection from the network to the subscriber is in the order of 2 to 6 Mbit/s and from the subscriber to the network in the order of 16 to 640 kbit/s.
The HDSL transmission technology relates to the transmission of a digital signal on the 2 Mbit/s level in a twisted pair cable. The HDSL technology is symmetric, in other words, the transmission speeds are equal in both directions. An individual HDSL transceiver system comprises transceivers which use echo cancellation technology and which are connected to one another via the two-way transmission path formed by the twisted pair cable. An HDSL transmission system can contain one, two or three such individual transceiver systems in parallel; in the case of two or three parallel pairs, the speed used in each parallel transmission connection is less than 2 Mbit/s; 784 kbit/s in the case of three parallel pairs and 1168 kbit/s in the case of two parallel pairs. International recommendations define how signals in the 2 Mbit/s level are transmitted in an HDSL system, such as, for example, the VC-12 signals of the SDH network or the 2048 kbit/s signals which comply with the CCITT recommendations G.703/G.704.
Because the aforementioned solutions only provide speeds in the order of 1 to 6 Mbit/s, the industry has also searched for a technology for the subscriber line that would provide ATM level speeds (10 to 55 Mbit/s). The international standardization organization ETSI (European Telecommunications Standards Institute) is in the process of creating a specification for VDSL (Very high data rate Digital Subscriber Line) devices which would make these kinds of speeds possible. VDSL technology can be used to implement both symmetric and asymmetric connections.
The aforementioned technologies that are used to transmit fast data via a twisted pair cable are referred to by the joint abbreviation xDSL. Therefore, even though it is not yet possible to provide broadband services to end users by using optical fiber, with these technologies teleoperators can provide the said services by using the existing subscriber lines. Because ADSL seems, at the moment, to be the most promising technology for implementation of broadband services, it is used as the example of the connection technology that provides the services.
The ADSL Forum has defined a network model relating to general xDSL connections. This model is illustrated in FIG. 1. The device which connects to the line at the user end is called ATU-R (ADSL Transmission Unit--Remote), and the device which connects to the line at the network end (in the local exchange) is called ATU-C (ADSL Transmission Unit--Central). These devices are also called ADSL modems (or ADSL transceivers) and they create an ADSL link between one another. The high-speed data of the ADSL connection are connected to the subscriber line so that the subscriber can still use the POTS services, but he or she is additionally provided with a high-speed data connection. These narrow- and broadband services are separated from one another by using a filter PS (POTS-splitter) which performs the frequency separation of ADSL signals and narrowband signals.
The terminals TE located at the end user can be of several types, for example, cable TV terminals TE1, personal computers TE2, or ISDN telephones TE3. For each terminal the system includes a service module SMi (i-1 . . . 3) which performs the functions related to terminal adaption. Such service modules can include, in practice, for example, so-called Set Top Boxes, PC interfaces, or LAN routers. The distribution network PDN (Premises Distribution Network) located in the premises of the subscriber connects the ATU-R to the service modules.
At the network end of the ADSL link the access node AN forms a concentration point for data, in which point the traffic which arrives from different service systems via different networks is concentrated. The access node is located, for example, at the central office.
In FIG. 1 the reference symbol A indicates the private part of the network, reference symbol B the public part of the network, and reference symbol C the network located at the subscriber premises.
The problem in a network of the type described above is how the end user is charged for the access service (i.e. for the use of the subscriber line) when he or she uses the services provided by the service systems, for example, Internet services. It is desirable that the charging is based on time or the volume of transmitted data, or both. The problem is caused, firstly, by the fact that the network can be connectionless. In other words, in this case the network does not feature messages for establishing and releasing a connection (such as SETUP and RELEASE), so the charging cannot be performed in the manner of the current telephone network on the basis of connection setup and release events. Secondly, the manufacturers of xDSL modems have not equipped their devices so that they could be used for charging on the basis of time or the volume of data transmitted. So it is not possible to query the modems for the information required for charging.
Let it be further noted that if the terminal is an ISDN or ATM terminal, each session is started with a SETUP message and finished with a RELEASE message, in which case time-based charging can be implemented by using the usual method. The aforementioned problem thereby relates to networks in which the network between the terminal and the access node, or at least for the link between the terminal TE and the delivery network PDN, is connectionless. Specifically, it is possible to implement the transmission path between the terminal and the access node, for example, in such a manner that the section between the access node and ATU-R is of the connection-oriented type (for example, ATM-based) and the section between the ATU-R and the terminal is connectionless (for example, an Ethernet link).
The problem is especially pertinent to the situation in which different customers use the same subscriber line because, in this case, the customers cannot be distinguished according to the subscriber line. This kind of a situation occurs, for example, when the general public is offered access to broadband services by placing the terminal in public premises, i.e., in a library or in a shopping center. The same problem is also encountered when it is desired, for example to work remotely (i.e. to telecommute) by connecting to the LAN of one's own employer only. In this case it is not possible either to detect that the charges for the access session in question should be addressed to the employer instead of the employee. The system cannot thereby distinguish when a person uses the connection as a so-called business user (whose charges are paid for by the employer) and when as a private user (who pays the charges himself or herself).
From now on the term "user" is used to refer to the person who uses the terminal, and the term "subscriber" is used to refer to the organization or person who pays for the use of the service. A user can also be a subscriber.